Planktonic Foraminifera As Oceanographic Proxies: Comparison of Biogeographic Classifications Using Some Southwest Pacific Core-Top Faunas

Home , Bounty Trough

Hindawi Publishing Corporation ISRN Oceanography Volume 2013, Article ID 508184, 15 pages http://dx.doi.org/10.5402/2013/508184

Review Article Planktonic Foraminifera as Oceanographic Proxies: Comparison of Biogeographic Classifications Using Some Southwest Pacific Core-Top Faunas

G. H. Scott

GNS Science, 1 Fairway Drive, Lower Hutt 5010, New Zealand

Correspondence should be addressed to G. H. Scott; [email protected]

Received 29 April 2013; Accepted 17 June 2013

Academic Editors: M. Elskens and M. T. Maldonado

Copyright © 2013 G. H. Scott. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The distribution of planktonic foraminifera, as free-floating protists, is largely controlled by hydrography. Their death assemblages in surficial sediments provide proxy data on upper water mass properties for paleoceanography. Techniques for mapping faunal distributions for this purpose are compared in a study of 35 core-top samples that span the Subtropical Front in the Southwest Pacific. Faunas are analyzed by taxon composition, order of dominant taxa, and abundance. Taxon composition (presence-absence data) and dominant taxa (ordinal data) recognize groups of sites that approximate major water mass distributions (cool subtropical water, subantarctic water) and clearly define the location of the Subtropical Front. Quantitative data (relative abundances) more closely reflect the success of taxa in upper water mass niches. This information resolves groups of sites that reflect differences in intrawater mass hydrography. Comparisons suggest that abundance data should provide much better oceanographic resolution globally than the widely used ordinal biogeographic classification that identifies only Tropical, Subtropical Transitional, Subpolar and Polar provinces. As the data are strongly structured by variance in the abundance of Globigerina bulloides, Globorotalia inflata, Neogloboquadrina incompta,andNeogloboquadrina pachyderma, comparable classifications result from most clustering strategies. Principal coordinates analysis best represents the configuration of sites in two dimensions.

1. Introduction planktonic foraminifera, Imbrie and Kipp [3]usedQ-mode factor analysis (QFA; [6]) to reduce the dimensionality of Although the diversity of the Holocene planktonic foraminif- n-taxoncore-topfaunalcountstoasmallnumberoffactor eral fauna is modest, many taxa are distributed through the assemblages. Each is a statistically distinct linear combination world ocean [1] and are exemplars for the interpretation of of the n-taxa. This simplifies the regression equation and Cenozoic oceans [2]. For paleoceanography, a primary goal is aids its interpretation. The ecological relevance of each fac- to classify Holocene faunas on the basis of their distributions tor assemblage was assessed by plotting the geographical andtorelatethemtothehydrography.Thebiogeographyof distribution of its contribution to each core-top fauna to show a single taxon can be simply mapped. The organization of sites according to their faunal content in a manner that is its relation to hydrography. While this provides a perspective informative for paleoceanography is a more complex task that on faunal biogeography, QFA does not identify discrete can be approached at several levels of analysis. Seminal works geographic/areal units based on faunal similarity. Rather, the in this field are those by Imbrie and Kipp3 [ ]andBe[´ 4]. underlying concept is a mixture model wherein a small num- Although they are widely applied and are similarly focused ber of notional source assemblages contribute to each core- on the distribution of dominant taxa, little attention has been top fauna. given to their quite different methods and to their suitability Much simpler methods were used by Be´ and Tolder- for resolving faunal biogeographies [5]. lund [7]andBe[´ 4]. From large databases of census data In developing a regression-based methodology for esti- from surface tows and sediment samples, they mapped mating sea surface temperatures (SST) from abundances of distributions of the major species and found regions where 2 ISRN Oceanography they occurred most abundantly. These data were integrated Local oceanic circulation tends to dominate the oceanic into a classification of five biogeographic provinces in the environment east of New Zealand. Subtropical water flows world ocean, principally defined by dominant taxa. The around the tip of North Cape and forms the south-eastward provinces correspond broadly to major global hydrographic flowing East Auckland Current [16]. This current extends as regions [8] and are bi-hemispheric. Although methodology far as East Cape before forming the southward-flowing East was not detailed, it transforms counts (quantitative data) to Cape Current [11, 17],whichisdeflectedeastwardbyChatham ranks (ordinal data). This simplifies the analysis of complex Rise. In this northern region, upper ocean circulation is abundance data. Ranks appear to have been determined also strongly influenced by three variable, semipermanent, by careful inspection of data rather than by an algorithm. anticyclonic eddies. In the south the Southland Current, As with QFA, dominant taxa are of primary importance, about 90% ASW [15]flowsaroundsouthernNewZealand but, in a conventional approach to biogeography, taxon and swings northward along the east coast of the South distributions are used to define discrete areal units. Unlike Island. Part of this flow turns eastward along the southern QFA, taphocoenses are interpreted as unitary faunas. flank of Chatham Rise, while a component continues north An important issue for planktonic foraminiferal biogeog- through Mernoo Saddle. Campbell Plateau is characterized raphy raised by the QFA method is whether it is realistically by weak mean flows but cyclonic flow is well developed portrayedwithamixturemodel.Aquestionraisedbythe around western Bounty Trough [18]. ordinal approach is whether there is significant loss of information when taxon abundances are reduced to ranks. These, and related topics, are addressed via the analysis of core-top 1.2. Previous Work. Kustanovich [19] recognized five bio- ∘ faunal data in the work of Weaver et al. [9] from a sector of geographic regions (Figure 2(a)) between 18–54 S, based on the Southwest Pacific east and south of New Zealand (36– species composition and dominance. Apart from the STF, no ∘ 61 S). The hydrography includes Subtropical Water (STW), relation between the hydrography and regional boundaries the Subtropical Front (STF), Australasian Subantarctic Water was noted. Eade [20] found that distributions of faunas in ∘ (ASW), and the northern front of the Antarctic Circumpolar plankton tows between 18–36 Swererelatedtotheprincipal Current (ACC). It provides a good basis for comparing faunal water masses. Several boundaries correspond closely to those regions with oceanography. of Kustanovich [19].Clusteranalysisoffaunalabundances in 234 surface sediment samples from the South Pacific by Parker and Berger [21]placedallfromtheNewZealand 1.1. Oceanographic Outline. Core-top samples come from a region in one group which spanned the STF (Figure 2(b)). region of diverse bottom topography and complex oceanog- This result may be related to the method used to calculate raphy spanning the transition from Subtropical to Sub- faunal similarity. antarctic water masses (Figure 1). There are two principal submerged continental blocks. Chatham Rise trends east for Although the scale of Be[´ 4,Figure7]preventsclose c.1300 km off central South Island. Depths at its crest are assessment, sites #1-2 of Weaver et al. [9] are in his Subtropical often <500m.SoutheastofSouthIslandisthevasttriangular Province. Remaining sites north of the STF and those in Campbell Plateau, mostly submerged between 500–1000 m. Bounty Trough are in the Transitional Province. The Polar Between these blocks is Bounty Trough, a failed rift. Bollons Province includes sites on Campbell Plateau. More details are Seamount rises over 2000 m above the abyssal Southwest shown in Figure 1 which treats line weights for taxa in Be[´ 4, Pacific basin off Campbell Plateau. Chatham Rise deepens Figure 8] as rank indices and applies them to Weaver et al. northward into Hikurangi Plateau, bordered on the west by [9, Table 3]. On this basis, seven of the eight faunas north theNewZealandplateboundary.Forcomparisonwithfaunal of Chatham Rise (Figure 1(a)) are identified as Transitional data,coresitesaregroupedintoNorthChatham,Bounty because Globorotalia inflata is the highest ranked species; Trough, and Campbell Plateau bathymetric regions. Site #35 Neogloboquadrina pachyderma and Globigerina bulloides are ∘ (61 S) is from the Southern Ocean. in second rank at several sites. Ten faunas in Bounty Trough The Subtropical Front (STF) lies over Chatham Rise. It is areallocatedtotheSubantarcticProvincebecauseGlobige- ∘ defined by surface temperature gradients of 4 C/200 km and rina bulloides is dominant. Neogloboquadrina pachyderma is strong along-rise currents [11–13]. Primary production in the in second rank in nine faunas. Six Campbell Plateau faunas frontal zone is high [14]. Flow from the north of warm, highly in which Globigerina bulloides is in first rank are classed as saline, nutrient-depleted Subtropical Surface Water (STW) Subantarctic. The remaining eight, with Neogloboquadrina ∘ extends south into the STF at ∼43 S. South of the STF is pachyderma in first rank, are identified as Polar. cold, less saline, nutrient-replete, Australasian Subantarctic Hayward [23] provided a taxonomic review of the fauna Water (ASW) covering Bounty Trough and Campbell Plateau. living in the New Zealand region and showed the distribution Thesouthernboundaryofthiswatermassismarkedatthe of taxa relative to Be’s´ [4] provinces. Martinez [22]recognized leading edge of the Antarctic Circumpolar Current by the three QFA assemblages in Tasman Sea core-tops. Principal −1 swift flowing (27–39 cms ) Subantarctic Front (SAF). The taxa in the factor 2 assemblage, which extended to the Southland Front, a local feature of the STF, separates a narrow vicinity of site #1 of this study (Figure 2(c)), are Globige- band of STW on the southeastern South Island shelf from rina quinqueloba and Globigerinita glutinata. Although the ASW [15]. assemblage was identified with the Transitional Province, ISRN Oceanography 3

QFA dominance maps Ordinal classification Transitional 80 East Auckland factor assemblage 35∘ S Current #1

80 #2 50

Current #4 #3 STW 20 ∘ 40 S Cape #5 Hikurangi 10 East Plateau #7 ODP Tasman Sea 1123 #6 #8 NCR (b) 1000 m Chatham Rise STF Subpolar factor MernooSaddle Chatham I. m #11 SCR #12 4000 assemblage ∘ 45 S #10 #9 10 STF Bounty #13 Current #14 #16 #17 #15 #18 m Trough 50 Campbell Southland 1000 m 80 Plateau #19

4000 #20 50 ASW Campbell #21 m Plateau#23 Bollons ∘ #22 1000 Seamount 50 S 1000 Trap 1

m #25 #24 (c) SAF #28 Polar factor #29 #27 #26 Trap 2 assemblage #30 #32 #31 #33 10 ∘ 55 S #34 20 #35 50

∘ 61 S 80 ∘ ∘ ∘ ∘ ∘ 165 E 170 E 175 E 180 175 W

Bé (1977) classification Transitional Polar Subantarctic

(d) (a)

Figure 1: (a) Core locations, bathymetry, circulation, and classification of core-top faunas in Weaver et al.9 [ ] following criteria in Be[´ 4]. To harmonize with the latter, Neogloboquadrina pachyderma coiling variants are combined with the p/d intergrade and Globigerina bulloides with Globigerina falconensis. (b)–(d) Dominance maps for factor assemblages in the FA-20 model [10]appliedtothesamedata(redrawnfrom [9, Figure 3]). Contours enclose areas in which factor loadings exceed the stated value. Loadings specify the percent variance in site faunas accounted for by each factor assemblage.

Globorotalia inflata is only a minor component. Weaver et al. 2. Data and Methods [9]appliedtheQFAmodelFA20ofMolfinoetal.[10]to the present data (Figures 1(b)–1(d)). Although the model I use data in Weaver et al. [9,Table3].Theycountedbetween was developed from Atlantic core-top faunas, the explained 241–552 specimens from the ≥150 𝜇m fraction in each sample. variance (communality) indicates that it is also applicable to Taxonomic categories are those of Imbrie and Kipp [3]. the Southwest Pacific faunas. Regions of highest dominance Core-top locations are shown in Figure 1.Analysesseekto ofthepolar,subpolar,transitional,andupwellingassemblages reveal the structure of the data (exploratory data mining). In approximated the principal oceanographic features. the absence of prior knowledge of data structure, the study 4 ISRN Oceanography

Kustanovich (1963) Parker and Berger (1971) Martinez (1994) Factor 2 dominance map Northern Fauna

North Central Fauna

Central Fauna 0

80 South Central Fauna 90 STF

Cluster I site (a) (b) (c)

Figure 2: (a) Faunal regions using the distribution and abundance of species in surface samples. Redrawn from Kustanovich [19, Figure 7]. (b) Cluster analysis of relative abundances of taxa in South Pacific surface sediments: distribution of Cluster I in the vicinity of New Zealand. Redrawn from Parker and Berger [21, Figure 7b]. (c) Dominance map of Factor 2 assemblage in a Q-mode analysis of core-top faunas principally north and west of New Zealand. Redrawn from Martinez [22, Figure 6b]; compare with Figure 1(b). uses unsupervized learning tools—cluster analyses and low- 3.2. Ordinal Data, Classification by Rank. Taxon abundances dimension projections. Each tool is referenced in its figure at each site are transformed to their rank order. Be’s´ [4,Figure caption. Kaufman and Rousseeuw [24] provide a readily 8] classification focused on major taxa. For comparison, accessible introduction to cluster analysis. Figure 3(b) shows a classification using the five highest ranks. Faunas are analyzed at three levels of complexity. At the The classification is similar to that using presence-absence primary level are species lists. Species ranked by their abun- data. North Chatham sites, excluding #1, form a well-defined dance (ordinal data) provide a second level of faunal repre- group with Globorotalia inflata in first rank. Sites in western sentation. Be[´ 4,Tables3,5–7; Figure 8] variously listed Bounty Trough form a low-level cluster; others join with sites species in rank order, identified dominant and cooccurring scattered across Campbell Plateau. All have Globigerina bul- taxa, and used line weights to show species importance in his loides in first rank and most have Neogloboquadrina incompta, faunal provinces. This suggests that his is an ordinal classi- Neogloboquadrina pachyderma, Globorotalia inflata in ranks fication. At a third level of analysis taxon, counts are treated 2-3. Sites on the southern margin of Campbell Plateau are as continuous variables (quantitative data), as in Imbrie and distinguished. All have Neogloboquadrina pachyderma in first Kipp [3]. rank. Southern Ocean site #35 is identified as an outlier, principally because Globorotalia inflata is in second rank. 3. Results 3.3. Quantitative Data: Projections and 3.1. Taxon Composition, Presence-Absence Classification. Classification by Abundance Taxon presence-absence data form two high-level clusters (Figure 3(a))thatarepartitionedabouttheSTF.The 3.3.1. Projections. By rotating the data matrix onto its prin- exception to this bathymetric/water mass separation is Site cipal axes, eigenvector methods provide two-dimensional #17 (Bounty Trough) which is placed with North Chatham views of the multivariate relative abundance data that often sites. A weaker boundary in the southern cluster partitions account for most of the variance. Singular value decomposi- most Bounty Trough sites from most Campbell Plateau tion (SVD, [27]) resolves the structure of the data by finding sites. Globigerina bulloides, Neogloboquadrina incompta, vector matrices that allow both objects (sites) and variates and Globorotalia inflata occur in all faunas (Figure 8). (taxa) to be projected onto the principal axes. The biplot Only slightly less persistent are Globigerinita glutinata and (Figure 4(a)) identifies species that are major sources of inter- Globorotalia truncatulinoides (s). Of remaining taxa, most site variation. The vector for Neogloboquadrina pachyderma is decrease in persistence from north to south. Northernmost associated with Campbell Plateau sites. Vectors for Neoglobo- site #1 has the most diverse fauna (21 taxa) and Southern quadrina incompta and Globigerina bulloides enclose Bounty Ocean site #35 has the least diverse (5 taxa). Trough sites and the vector for Globorotalia inflata is in ISRN Oceanography 5

Presence absence Ordinal 8 80

6 60

4 40

2 1 20 s

35 s 7

0 14

29 12 0

North Chatham Campbell Plateau North Chatham Campbell Plateau Bounty Trough s Southern Ocean Bounty Trough s Southern Ocean (a) (b)

Figure 3: (a) Agglomerative classification of sitesFigure ( 1) using presence-absence data with function agnes(). Euclidean metric, Ward cluster strategy. Agglomerative coefficient = 0.83. (b) Agglomerative classification of sitesFigure ( 1) using ordinal data. Taxa ranked with function daisy(). Sites clustered using five highest ranked taxa using function agnes(). Euclidean metric, Ward cluster strategy. Agglomerative coefficient = 0.86. Functions are in R package cluster available from http://cran.r-project.org/web/packages/cluster/.

the direction of North Chatham sites. Distances between 3.4.1. Hikurangi Biotope (HB). Included are sites #2–8 from sites projected onto the principal axes in the principal the North Chatham bathymetric region. In all views of the coordinates analysis (Figure 4(b))approximatethoseinthe data, the southern boundary coincides with the STF. Faunas similarity matrix [28]. Nonmetric multidimensional scaling have between 12–17 species. In all faunas Globorotalia inflata (Figure 4(c);[29]) operates on the rank order of similarities is commonest taxon, followed either by Globigerina bulloides between sites; these are reflected in the two-dimensional plot. or Neogloboquadrina incompta.Onlyatsite#6doesGloboro- All projections show Southern Ocean site #35 as an outlier. talia truncatulinoides (s)moveashighasthirdrank.Itisafirst Sites #1 and #17 lie between the major groups. ranktaxonintheTransitionalProvinceofBe[´ 4]. Although rankings of leading taxa are relatively stable, the abundance of Globorotalia inflata varies greatly (39–80%). This affects 3.3.2. Classification. Although projections indicate that sites the configuration of HB sites in Figure 4(a),contributesto are clustered, some are poorly delimited, as is their num- a low average silhouette width in the fuzzy classification ber. Cluster validation (Figure 5(a)) indicates that clusters (Figure 5(a)), and to high-level linkages of subgroups in the resolved by several strategies are maximally compact (silhou- consensus classification (Figure 5(d)). ette index, [24]) when there are 3–5 groups. The 4-group ∘ fuzzy classification (Figure 5(b))showsthatBountyTrough HB1. Sites #2, #5, and #8. These are located between 36–43 S and Campbell Plateau sites form the most compact groups. atslopedepthsnearNorthIsland.Theyareinthevicinity Measured by their silhouette widths, sites #1 and #17, already oftheEastCapeCurrent.AlthoughGloborotalia inflata identified as intermediates in some projections (Figures 3(a) and Globigerina bulloides maintain their rank positions, the and 3(b)), are poor fits as are southern Campbell Plateau abundance of the latter (19–22%) is higher than elsewhere in sites #25, #26, and #30. The hierarchical agglomerative the region. classification (Figure 5(c)) produces three high-level groups that correspond to the North Chatham, Bounty Trough, and HB2.Sites#3,#4.Globorotalia inflata is strongly dominant CampbellPlateaubathymetricregions.Site#1ismappedasan (65–80%) at these deep sites (3654 m, 3003 m) on Hikurangi outlier in the North Chatham region. Western Bounty Trough Plateau. No other species exceeds 11%; faunas are the least sites are tightly clustered and distinguished from sites #18 and equitable in the biotope. The sites are outliers in projections #22atitseasternmargin.Site#17,apoorfitinFigure 5(b), (Figure 4). is allocated to its source bathymetric region. Southern sites form a low-level group within the Campbell Plateau cluster. HB3. Sites #6, #7. Although site #7 is higher on the northern flank of Chatham Rise than is site #6, they form a low- level cluster in dendrograms (Figure 5). Neogloboquadrina 3.4. Regional Biogeography. The regional biogeography incompta (25–31%) is much more abundant than in other (Figure 6) considers results from all views of the data but subregions. is based primarily on classifications with quantitative data. It recognizes 3 biotopes, several with subbiotopes. Units Outlier. Site #1 has the most species-rich fauna (21 taxa). are based on faunal similarity, with the constraint that sites In composition, it is grouped with other North Chatham within the same unit are adjacent. sites but with ordinal data it is linked to Bounty Basin sites 6 ISRN Oceanography

0.4 60 35 Pachy 35 3 Campbell Plateau (s) 0.3 4 40 33 34 31 30 26 29 0.2 34 20 8 20 2132 33 31 5 2728 25 North2 Chatham 23 24 26 6 0.1 25 QuinquelobaBulloides Glutinata 30 7 0 trunc (s) 1914

15111816910 Bounty Campbell 20 21 1 SVD 1 SVD 22 PCO 2 13 12 Trough 0 Plateau 1 Pachy 29 23 17 17 32 − (d) 22 20 27 24 − 52 7 0.1 86 28 18 15 −40 Inflata 13 4 −0.2 19 11 14 12 3 1610 9 North Chatham Bounty Trough −60 −0.3 −60 −40 −200 204060 −0.3 −0.2 −0.1 0 0.1 0.2 0.3 SVD 2 PCO 1 (a) (b) 35 0.4

Campbell 33 Plateau 31 34 North Chatham Bounty Trough 0.2 30 26 1 S804 9 Q220 17 Q217 29 2 H211 10 H347 18 Q582 202132 2527 3 Q859 11 Q216 19 H564 282324 4 S938 12 U938 22 Q585 5 P69 13 Q215 22 6 S924 14 Q203 0 Bounty 1914 18 1 Trough 1191016 7 R657 15 Q208 NMS 1 121513 17 8 U951 16 Q200 2 5 Campbell Plateau Southern Ocean 7 8 North Chatham 20 F104 29 36–41 35 50–33 −0.2 6 4 21 F111 30 16–9 23 D84 31 36–40 24 F149 32 B32 3 25 D206 33 34–1 26 F137 34 36–39 27 D178 −0.4 28 36–42 −0.4 −0. 2 0 0.2 0.4 NMS 2 (c)

Figure 4: Projections of sites onto principal axes for two largest eigenvalues. (a) Singular value decomposition (SVD), vectors are projections of major taxa; 87% variance shown. (b) Principal coordinates analysis; 53% variance shown. (c) Nonmetric multidimensional scaling, Euclidean distances. All computed with PAST v1.11 (http://folk.uio.no/ohammer/past/) Site identifiers [9,Table1]aregroupedbybathymetric regions.

(Figure 3). Important contributors to its distance from commonly lower than in HB faunas. Minor species in the lat- other North Chatham faunas using quantitative data are ter that are not recorded here are Globigerinella aequilateralis, the reduced abundance of Globorotalia inflata (17%, third- Globigerinoides sacculifer, Neogloboquadrina dutertrei,and ranked) and strong representations of Globigerina bulloides Pulleniatina obliquiloculata. No fauna is strongly dominated (20%) and Globigerina falconensis. by one species and species distributions are more equitable than in HB. 3.4.2. Bounty Biotope (BB). Sites #9–16, #18-19, and #22 form a compact group in all projections and classifications. Of BB1. Sites #9–16, #19. These sites are under a local gyre in ASW Bounty Trough sites, only #17 is excluded. Diversity (8–16) is and have closely similar faunas. They form a tight cluster in ISRN Oceanography 7

Validation

Agglomerative Fuzzy classification 27 k Medoid 32 means Divisive 9 21 13 20 0.40 Fuzzy 0.6 10 111612 2829 1419 23 4 15 24 5 8 3 0.4 2 18 0.35 6 35

Silhouette 31 7 34 0.2 33

Silhouette 22 0.30 0.0

1 26 − 2345678 0.2 17 30 Number of clusters 25 (a) (b)

Agglomerative classification Consensus classification 2.0 80 1.5 60 1.0 40 0.5 s 35 20 1 0.0 0 s 17 4 3 31 8

1 3 7 4 8 9 2

6 5 6 7 34

29 32 23 20 24 25 27 26 31 33 12 13 34 14 35 15 10 21 11 19 28 17 18 30 16 22 18 23 22 15 12 24 26 25 2 5 16 9 33 30 32 29 13 14 19 28 27 10 11 20 21

North Chatham Campbell Plateau North Chatham Campbell Plateau Bounty Trough s Southern Ocean Bounty Trough s Southern Ocean (c) (d)

Figure 5: Classifications using relative abundance data. (a) Optimal number of clusters for five strategies in R package clValid; see http://cran.r-project.org/web/packages/clValid/vignettes/clValid.pdf for details. Silhouette width (Kaufman and Rousseeuw [24]measuresthe difference between the distance of the site to the nearest-neighbor group and its distance from others in the same group. The higher the index is on the −1 to +1 scale the better is the site classified. (b) Silhouette plot of fuzzy classification using function fanny(); four groups specified, euclidean metric. Agglomerative classification with function agnes(). Euclidean metric, Ward cluster strategy. Agglomerative coefficient = 0.92. (d) Consensus hierarchical classification that synthesizes dendrograms produced by Ward, single, complete, average, mcquitty, median, and centroid cluster methods; see http://cran.r-project.org/web/packages/clue/vignettes/clue.pdf for detail.

quantitative classificationsFigure ( 5). In all, Globigerina bul- Weaver et al. [9] considered that site #17 might not represent loides is dominant (32–40%) and Neogloboquadrina incompta true core-top material. (12–25%) and Globorotalia inflata (11–18%) are second or third ranked. 3.4.3. Campbell Biotope (CB). Species diversity (7–10) in Campbell Plateau faunas is commonly lower than in Bounty BB2. Sites #18, #22. Site #22 is adjacent to Bollons Seamount Trough faunas. There are no records of Globigerina calida, and,likesite#18,isadeepsiteatthemarginoftheSouthwest Globigerina digitata, Globigerinoides tenellus, Globorotalia Pacific Basin. Both are differentiated from other BB sites by crassula,andGloborotalia hirsuta. Sites are rather homoge- greater abundance of Globigerina bulloides (47–49%). neous in faunal composition.

Outlier. The composition of the site #17 fauna is similar to CB1. Sites #20-21, #23-24, #27–29, and #32 form a compact that at some HB sites (Figure 3(a)). Another similarity is group (Figure 5(b)). As in BB, Globigerina bulloides (34–44%) the abundance of Globorotalia inflata (33%). Griggs et al. is the first-ranked taxon but Neogloboquadrina pachyderma (1983) [30] found evidence of dissolution in this core (Q217). (23–35%) displaces Neogloboquadrina incompta (3–10%) in 8 ISRN Oceanography

Globorotalia 17 42 ∘ inflata 35 S #1 6580 60 45 42 40 51 39 #2 1313 13 11 13 13 18 33 12 19 STF 12 9 12 28 #4 #3 16 ∘ HB1 HB2 18 12 20 40 S 5 7 7 10 HB 3 5 #5 10 10 11 3 #6 10 SAF HB3 #8 #7 1000 m (b) m #9 #11 4000 ∘ #12 Neogloboquadrina2 45 S #10 incompta 4 BB1 #13 #14 9 10 #15 6 6 20 31 #16 #17 #18 25 m 12 #19 18 1000 m 22 25 BB2 20 4000 15 20 12 23 12 15 10 STF 14 #20 5 3 m 5 #22 9 #21 BB 7 7 50∘ #23 10 6 S 3 9 1000 7 2 2 #25 #24 1000 1 2 m SAF #28 #27 CB1 #29 #26

(c) N. 0 #30 pachyderma 0 #32 CB #31 0 0 0 Globigerina 20 CB2 0 19 bulloides #34 #33 1 0 ∘ 4 11 3 55 S 4 6 0 1 6 5 5 3 19 5 7 5 22 16 10 STF 7 34 20 33 10 36 30 30 26 32 10 40 38 32 40 39 31 26 34 23 33 47 2428 STF 35 40 36 44 30 36 49 34 50 31 50 40 24 40 52 50 42 26 61∘ SAF 44 39 S 38 20 42 25 #35 30 35 SAF (e) ∘ ∘ ∘ ∘ 165 E 170 E 175 E 180

(d) (a)

Figure 6: (a) Regional biogeography constructed from data in Figures 3–5. Site #35 is identified as an outlier but would likely classify as polar in a more inclusive higher southern latitude survey. Similarly, site #1 may represent the Northern Fauna of Kustanovich [19]. (b)–(e) Abundance plots for Globorotalia inflata, Neogloboquadrina incompta, Globigerina bulloides, and Neogloboquadrina pachyderma.Approximateposition of the STF and SAF after Northcote and Neil [26, Figure 1]. second rank. Very similar faunas occur at widely separated the consensus classification (Figure 5(d)), although the fuzzy sites across the plateau. classification (Figure 5(b)) indicates that the relation is weak.

CB2.Sites#30-31,#33-34atthesouthernmarginofCampbell Outlier. Southern Ocean site #35 has the least diverse fauna (5 Plateau are separated from other CB faunas in the projec- taxa), but its composition is similar to some southern CB sites tion (Figure 4(a)) and unified in quantitative classifications (Figure 3(a)). The position of Globorotalia inflata in second (Figures 5(c) and 5(d)) primarily by increased abundance of rank distinguishes the fauna from those in CB2 (Figure 3(b)). Neogloboquadrina pachyderma (50–52%). Faunas in southern But it is the dominance of Neogloboquadrina pachyderma interior plateau sites #25-26 have lesser representations of (86%) that distances the fauna from others in projections and Neogloboquadrina pachyderma. They link with this group in classifications (Figures 4 and 5). ISRN Oceanography 9

4. Discussion Table 1: Relationships between faunas in sediment traps and nearby core-topsamples.NCRandSCRdataarefromKingandHoward 4.1.TheSubtropicalFrontasaSpeciesBoundary:TaxonDistri- [25]. Trap 1-2, TAN0307, and SO136 data are from Northcote and butions. Taxon composition is the primary carrier of faunal Neil [26]. Pearson 𝑟 measures linear relationship in quantitative data; information. Although many planktonic foraminiferal taxa Kendall tau measures monotonic relationship in ranked data. Taxa have wide meridional distributions [1] and the STF appears that did not occur in either sample were excluded from the data. to be a “leaky” boundary between STW and ASW [12], pres- Kendall Prob. tau = 0 Pearson 𝑟 Prob. 𝑟=0 ence-absence data define its location very clearly. Compar- tau ison of taxon distributions (Figure 8)withthehierarchical NCR300:NCR1000 3.65𝐸 − 04 0.99 5.03𝐸 − 13 classification (Figure 3(a)) shows that its location is better 0.67 1.23𝐸 − 11 defined by a mapping that considers all taxa than by any NCR1000:Site #8 0.28 0.144 0.98 pairwise comparison of taxon ranges. NCR1000:Site #7 0.36 0.068 0.91 1.17𝐸 − 06 The persistence of taxa reveals some aspects of the STF as SCR300:SCR1000 0.66 0.004 0.87 1.97𝐸 − 04 a faunal boundary. Taxa that are present at all STW sites (per- SCR300:Site #12 0.55 0.037 0.63 0.052 > sistence = 100%) are highly persistent ( 80%) in ASW south SCR1000:Site #12 0.82 4.65𝐸 − 04 0.91 5.18𝐸 − 05 of the front. Excepting Globigerina digitata,taxapresentin Trap 1:Trap 2 0.64 0.001 0.55 0.034 at least one of the three southernmost sites under STW (#6–#8) are present in ASW. Globigerinella aequilateralis, Trap 1:Site #21 0.56 0.023 0.35 0.287 Globigerinoides sacculifer,andGlobigerinoides tenellus occur Trap 1:Site #24 0.46 0.051 0.43 0.158 only at northern STW sites (#1–#5). Globigerina quinqueloba Trap 1:Site #25 0.41 0.098 0.42 0.201 and Neogloboquadrina pachyderma are highly persistent in Trap 1:Site #27 0.34 0.181 0.28 0.412 ASW,but their persistence in STW declines to 37–50%. While Trap 1:TAN0307 0.37 0.173 0.11 0.761 these observations are dependent on sample size (taxa whose Trap 2:SO136 0.37 0.045 0.06 0.804 population abundance is <2% are unlikely to be represented Trap 2:Site #24 0.26 inthesmallestsamplecounted(𝑛 = 241)), they suggest 0.65 0.002 0.346 that the faunal composition boundary between STW and ASW faunas is much broader than the STF as defined by physical hydrography [31]. Particularly, some subtropical taxa Sites #7 and #8 are in the vicinity of sediment trap become very impersistent or disappear from the core-top NCR [25] just north of the STF. In these core-top faunas, ∘ record about 40 S. If species abundances are also considered, respectively, at 1408 m and 850 m, abundances of major taxa the STF acts like a high-pass filter that removes taxa with that may have accumulated over as much 1850 years [9] small populations. are comparable with those recorded over 11 months at NCR (null hypothesis rejected using Pearson 𝑟). This suggests that annual variance in abundance has been dominant and stable, 4.2. Ordinal Classification and Taphonomy. Transformation relative to interannual variance [35], and taphonomic effects of abundances to ordinal data reduces variance and, there- are minimal. Trap SCR is near the southern margin of the STF fore, information. Here, classification of sites by ordinal in Bounty Trough [25]. The fauna trapped over 8 months at data only marginally improves the resolution of groups 1000 m is similar to that at site #12. In quantitative and ranked (agglomerative coefficient = 0.86) over the presence-absence comparisons, the null hypothesis is strongly rejected. Again, analysis (0.83). Neither level of analysis performs as well as no significant degradation of the living signal is detected in quantitative data. This suggests that, for classification, there is the fossil core-top fauna. There are no data on the age of core- little value in transforming abundance data to ordinal. From top faunas in this region. Northcote and Neil [26]reported an analysis of Imbrie and Kipp’s [3] data transformed to ranks, on faunas collected over 14 months in their sediment Trap Sancetta [32] found that they identified assemblages almost 1,sitedinthethermallyisolated,relativelyquietwaterofthe identical with those produced with quantitative data. How- interior of Campbell Plateau and in Trap 2 on its current- ever, her ranks do not represent strictly ordinal data. They swept eastern margin (Figure 1). Faunas at both sites differed were constructed by assigning ranks to binned percentages significantlyfromthoseinnearlycore-tops.Thisisconfirmed rather than ordering abundances by <,=,> relationships. for quantitative data; the null hypothesis is not rejected at Ordinal data are also of interest because Kidwell [33] the 5% level in any of the five comparisons. Correlation found that fossil mollusc faunas commonly preserve the coefficients are higher for ranked data; for sites #21 and #24 species rank signal of their source living faunas and may the null hypothesis is rejected at the 5% level. Radiocarbon mitigate the effects of taphonomy and time averaging on dates (yr BP, data from Christine Prior, GNS) for Globigerina quantitative data [5, 34]). A few local data are relevant. bulloides (5524), Globorotalia inflata (4582), and Globorotalia Table 1 lists Pearson 𝑟, a measure of linear relationship in truncatulinoides (3919) from site #21 suggest that, for this quantitative data, and Kendall tau, a measure of monotonic middle Holocene fauna, ranked data better preserve the Trap association in ranked data, between faunas from sediment 1 faunal signal than do quantitative data. traps and nearby core-tops. Of interest is whether ranked data indicate association between living and core-top faunas when 4.3. Quantitative Classifications and QFA. Organization of quantitative data do not. sites is substantially raised (agglomerative coefficient = 0.92) 10 ISRN Oceanography

Factor 2 assemblage Site #3 Fauna North Chatham 1.0 100

0.5 50

Factor score

Relative abundance Relative

0 0

) ) ) )

) )

s s s

d d

p/d p/d

a (

Ruber

Inflata Inflata

Calida Calida

Scitula Scitula

Hirsuta Hirsuta

Tenellus Tenellus

Digitata Digitata

Crassula Crassula

Universa Universa

Bulloides Bulloides

Dutertrei Dutertrei

Incompta Incompta

Glutinata Glutinata

Falconensis Falconensis

Unidentified Unidentified

Quinqueloba Quinqueloba

Crassaformis Crassaformis

Sacculifera w Sacculifera w

Aequilateralis Aequilateralis

Sacculifera wo Sacculifera w

Obliquiloculata Obliquiloculata

Pachyderma ( Pachyderma

Pachyderm

Truncatulinoides ( Truncatulinoides ( Truncatulinoides

Truncatulinoides ( Truncatulinoides ( Truncatulinoides (a) (b) Average Fauna Hikurangi Biotope 100

Relative abundance Relative

) )

)

s s

p/d

Ruber

Inflata

Calida

Scitula

Hirsuta

Tenellus

Digitata

Crassula

Universa

Bulloides

Dutertrei

Incompta

Glutinata

Falconensis

Unidentified

Quinqueloba

Crassaform

Sacculifera w

Aequilateralis

Sacculifera w

Obliquiloculata

Pachyderma ( Pachyderma

Truncatulinoides ( Truncatulinoides

Truncatulinoides ( Truncatulinoides (c)

Figure 7: (a) Taxon scores in factor 2 assemblage from Q-mode factor analysis of Weaver et al. [9, Table 3] using Paleo ToolBox http://www .pangaea.de/software/files/Windows/PaleoTools/. (b) Relative abundance of taxa at site #3 (Figure 1); this fauna is an outlier in projections (Figure 4). (c) Relative abundance of taxa in average HB fauna (Figure 6). when relative abundances of taxa are analyzed. These data are the provincial approach is holistic and treats faunas as a much more sensitive measure of species success in near- units whereas QFA decomposes faunas into nominal source surface niches than are species ranks. Like water mass differ- assemblages. This identifies it as a method for analyzing entiation, groups of sites within water masses are identified mixtures [36] rather than for mapping the areal distribution that may indicate local contrasts in hydrography. Some are of faunas. Each factor assemblage represents a statistically related to bathymetry, as with Bounty Trough and Campbell independent notional source fauna. All site faunas are mod- Plateau faunas. These second order features are not resolved elled as mixtures of these source faunas. Core-top faunas are in QFA dominance maps (Figures 1(b)–1(d)). taphocoenoses. Although some specimens may be advected The provincial approach to biogeography of Be[´ 4]and in zonal jets and eddies, shell sinking velocities of ∼500 m/day QFA models based on Imbrie and Kipp [3]areclearly [37, 38] imply that most core-top faunas are from populations distinguished by their levels of data analysis. The former is living near the site. Therefore, studies that apply QFA to core- ordinal; the latter is quantitative. Perhaps more importantly, top faunas seek to resolve statistically independent faunas in ISRN Oceanography 11

)

( (d)

inflata

calida

bulloides quinqueloba aequilateralis falconensis digitata

glutinata ruber w ruber sacculifer w sacculifer tenellus universa pachyderma incompta obliquiloculata crassaformis dutertrei scitula truncatulinoides pachy/dutertrei sacculifer w sacculifer hirsuta truncatulinoides unidentified crassula Site # 1 2 3 4 5 6 7 8 North Chatham Subtropical front 9 10 11 12 13 14 15 16 17 18 Trough Bounty 19 22 Bathymetric boundary within Australian subantarctic water 20 21 23 24 25 26 27 28 29

30 Plateau Campbell 31 32 33 34 Subantarctic front 35

SO Figure 8: Taxon distribution. Nomenclature as in [9]. the overlying water column. Principal scenarios are vertical dominates a factor assemblage (Figure 7(a))resolvedbyQFA stratification and seasonal replacement [3,page83].For of the Weaver et al. [9] data. It corresponds to the Transitional oceanography, unmixing of core-top faunas to identify their assemblages of BeandHutson[´ 40] and Molfino et al. [10]. source populations in the water column is valuable but should The distribution of factor scores compares well with rela- be distinguished from primary-level biogeographic mappings tive abundances of taxa at site #3 (Figure 7(b))whichisa that accept core-top faunas as unitary entities. divergent fauna (Figure 4). Although Globorotalia inflata is Varimax rotation [39] is a critical component in Imbrie dominant, the average HB fauna (Figure 7(c))ismorediverse and Kipp’s [3] method. It rotates the principal axes of the data and equitable. The dominance map for this factor assemblage matrix to positions close to vectors for the most divergent effectively shows the distribution of a single species. The value faunas. Such faunas include the most atypical. Some are of this approach for resolution of vertical stratification and/or highly inequitable with one strongly dominant taxon. They seasonal mixing faunas in core-top faunas is equivocal. In identify pelagic environments with few resources for most view of the source of core-top faunas, it seems logical that taxa. Some may be in water masses distant from the core-top the training sets for mixture analysis should be data on living faunas being unmixed. Often, names which are attached to faunas collected at various depths/seasons in the same water the factor assemblages (e.g., Molfino et al. [10] are related to mass. theprovincialnomenclatureofBe[´ 4]).Sonamed,dominance maps may suggest substantial advection and misleading 4.4. Taxa as Hydrographic Proxies. Related to their food hydrographic scenarios. sources, planktonic foraminiferal species tend to preferen- Although varimax rotation simplifies data interpretation tially occupy particular niches in the upper ocean [41]so [3, 10], the realignment of principal axes towards divergent havethepotentialtoprovideproxydataonnear-surface faunas may generate factor scores that significantly misrep- hydrography. Data on taxa contributing largely to variance resent faunas in a water mass. Globorotalia inflata strongly in abundance data (Figure 4) are noted. Their distributions 12 ISRN Oceanography are more directly interpretable as hydrographic proxies than much greater in STW than in ASW. The STF marks a sharp are the corresponding factor assemblage dominance maps (cf. decline in its abundance (Figure 6(b)). It is strongly dominant Figures 1(b)–1(d) and Figures 6(b)–6(e)). in HB2 which is in the vicinity of the STF region [49] Globigerina bulloides lacks symbiont algae and is primar- and features relatively high chlorophyll-a concentrations and ily a herbivore although it is also a zooplankton predator winter deepening of the mixed layer. Although its abundance [42]. It is abundant in near-surface water when biomass is at site #3 in HB2 may be enhanced by dissolution [9,Figure high, as in upwelling pulses [43]. Kincaid et al. [44]found 2]), the biotope possibly captures a strong trophic signal. that its abundance is correlated with phytoplankton blooms. Globorotalia inflata maintains quite uniform abundances (10– Vertically stratified plankton tows in the Southern Ocean 20%) in most Bounty Trough and Campbell Plateau faunas. ∘ between 41–53 S[45] show its abundance covaries closely Only at the southwest margin of the latter are they <10%. with fluorescence maxima, a biomass proxy, in near-surface These data, which are consistent with those collected from ∘ water. Schiebel et al. [46] found that its abundance is closely traps between 47–54 SnearTasmania[56], contrast with related to entrainment of nutrient-rich water. The primary its 62% abundance in Trap 1 at Pukaki Rise (Figure 1). domain of Globigerina bulloides is in ASW (Figures 1 and ThisishigherthanitsaverageinHB(49%).InBBand 6(d)). Rather uniform abundances in BB and CB indicate CP core-top faunas it is most abundant at site #17 (33%) similar resource availability in the macronutrient-rich low- which similarly has Globigerina bulloides in second rank. chlorophyll mixed layer over Bounty Trough and Campbell Although quantitative data strongly differentiate the Trap 1 Plateau [26]. Larger populations at deep water sites east of fauna, several core-top faunas are comparable in rank tests Bounty Trough (BB2) and around the margin of Campbell (Table 1). Globorotalia inflata is widely distributed through Plateau may reflect turbulent entrainment of nutrients into ASW and is the third-ranked taxon in several CB faunas. the mixed layer. Although its abundance is often related Trap 1 data [26]showthatlargerpopulationsseasonally to algal biomass, the taxon shows no response to elevated occupyCampbellPlateaubutknowledgeoftheirsize,age- chlorophyll-a levels associated with the STF [47]. This may structure, and taphonomy over longer intervals is required to relate to the composition of the flora. Small-celled species, understand this response. particularly nanoflagellates, predominate in ASW whereas Neogloboquadrina pachyderma was trapped mainly ∘ ∘ floras about the STF are dominated by diatoms48 [ ]. At sites between 0–100 m at Southern Ocean sites (50 S, 53 S), near under STW, the taxon is most abundant nearest North Island the polar front zone [45], but was principally present between (HB1), possibly responding to high nutrient levels near the 75–200 m, below the fluorescence maxima at some northern ∘ shelf break, and at site #1. It is notably rare in HB2, near a sites (41–47 S).Kohfeldetal.[57] showed that shells calcified region with high chlorophyll-a concentrations [49]. at surface water temperatures in the Southern Ocean. Food From three Northern Hemisphere trap studies, Sautter sources include diatoms [58]. This taxon dominates Southern and Thunell [43]foundthatNeogloboquadrina incompta Ocean faunas, of which site #35 is representative. It is less was primarily located within or below the thermocline and dominant (∼50%) in CB2 faunas at sites around the southern was responsive to heightened fertility. Pak and Kennett margin of Campbell Plateau. These locations are at the [50] showed that it calcifies near the thermocline. Reynolds leading edge of the ACC where the SAF meets Campbell and Thunell [51] and Sautter and Sancetta [52]notedthat Plateau [18] and the taxon’s abundance may reflect mixing populations increased when near-surface water was weakly with ASW. Over Campbell Plateau, it contributes between stratified. Its abundance at 1000 m at trap SCR in Bounty 20–40% of most faunas but sharply declines to ≤10% at its Trough [25] compares with those in nearby core-tops (∼20%– northern margin. This clearly defined bathymetric relation 25%) but drops to 2% at 300 m. Unlike Globigerina bulloides, indicates that population size is not directly linked to SST, as the taxon is most abundant about the STF where it may reflect is commonly suggested. It is a minor contributor to Bounty fertility in the vicinity of the thermocline. It is common in Trough faunas and drops below sample resolution at site all Bounty Trough sites but is more populous adjacent to #12, as it does in most HB faunas. Indeed if, as Darling et al. the margin of the STF (sites #11, #12) than at the southern [59]found,asmuchas1.5%ofNeogloboquadrina incompta margin of the trough (sites #16, #19). Although its abundance coil sinistrally, Neogloboquadrina pachyderma may not be map (Figure 6(c)) identifies the location of the STF, large present in HB faunas. populations particularly characterize the northern margin (HB3). As in the Benguela region [53] this may relate to the distribution of a specific diatom food resource [54]that 5. Conclusions flourishes at the margin of highly productive water. Globorotalia inflata is a deep-dwelling omnivore that lives Be’s´ [4] provincial biogeography of planktonic foraminifera on diatoms, dinoflagellates, and animal tissue [40, 41]. The is viewed as an ordinal classification that treats faunas holis- ∘ largest population in stratified traps at 41 S(AtlanticOcean, tically. QFA operates on quantitative data and seeks to resolve [45]) was between 200–300 m, well below the fluorescence faunas into source assemblages. The two methods are distinct maximum at ∼50 m. With stable isotope data for trapped in their level of analysis and in their objective. Their outputs specimens from STW through to Antarctic Surface Water, are not directly comparable. King and Howard [55] inferred calcification depths between QFA is a tool for mixture analysis rather than for mapping 0–100 m. Its record in Traps NCR and SCR [25](Figure 1) regional biogeographies. It treats all core-top faunas as is consistent with the HB data. Its relative abundance is composites of nominal assemblages. These are modelled on ISRN Oceanography 13 the most divergent faunas in a core-top dataset. It is question- 103–122, Kluwer Academic Publishers, Dordrecht, The Neth- able whether there is a valid ecological rationale for their use lands, 1999. as prototypes in preference to the statistics of living faunas. [6] K. G. Joreskog,¨ J. E. Klovan, and R. A. Reyment, Geological ∘ Analyses of core-top faunal distributions from 35–61 S Factor Analysis, Elsevier, Amsterdam, The Netherlands, 1976. in the Southwest Pacific show that presence-absence and [7]A.W.H.Be´ and D. S. Tolderlund, “Distribution and ecology of ordinal data detect the STF but are much less effective living planktonic foraminifera in surface waters of the Atlantic than quantitative data for identifying lesser hydrographic and Indian Oceans,” in The Micropaleontology of Oceans,B. features. 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Their distribution may not be as simple as [9]P.P.E.Weaver,H.Neil,andL.Carter,“Seasurfacetemperature presently envisaged [5]. estimates from the Southwest Pacific based on planktonic Biotopes in the transect reflect variation in the abundance foraminifera and oxygen isotopes,” Palaeogeography, Palaeocli- matology, Palaeoecology,vol.131,no.3-4,pp.241–256,1997. of four dominant taxa which relate to the distribution and structure of water masses. Deep-dwelling Globorotalia inflata [10]B.Molfino,N.G.Kipp,andJ.J.Morley,“Comparisonof Foraminiferal, Coccolithophorid, and Radiolarian paleotem- characterizes the STW biotope. Two biotopes are recognized perature equations: assemblage coherency and estimate concor- in ASW south of Chatham Rise. In both, a nutrient-rich dancy,” Quaternary Research,vol.17,no.3,pp.279–313,1982. mixed layer is indicated by similar abundances of Globigerina [11] R. A. 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